Camera: Extend vendor tag helper methods

Allow 'CameraMetadata' clients to query the vendor id for the
respective 'camera_metadata'.
Allow vendor tag cache clients to check the descriptor availability.

Bug: 164187235
Test: Manual using TestingCamera2,
Camera CTS

Change-Id: I463c1e091bc60e71549e10fbbe836fb1d714e890
diff --git a/camera/CameraMetadata.cpp b/camera/CameraMetadata.cpp
index 135384a..7e4c91e 100644
--- a/camera/CameraMetadata.cpp
+++ b/camera/CameraMetadata.cpp
@@ -22,6 +22,7 @@
 
 #include <binder/Parcel.h>
 #include <camera/CameraMetadata.h>
+#include <camera_metadata_hidden.h>
 
 namespace android {
 
@@ -872,5 +873,8 @@
     return OK;
 }
 
+metadata_vendor_id_t CameraMetadata::getVendorId() {
+    return get_camera_metadata_vendor_id(mBuffer);
+}
 
 }; // namespace android